This invention relates to a closure for closing the top opening of a gas offtake pipe having a circular or oval cross-sectional configuration and disposed on the roof of a coke oven to conduct raw gas evolving in an oven chamber during the coking of coal to a main. More particularly, the closure of the present invention includes a domed top cover having a peripheral edge arranged to dip into a water seal provided on the top edge of the gas offtake pipe when the cover is in the closed position and an inner cover having an edge to engage with an inner support surface of the gas offtake pipe.
Problems have been encountered with a closure of this type for a gas offtake pipe because the inner cover embodies a cast iron construction which is very heavy and necessitates the provision of counter weights for actuating linkage when opening or closing the cover. Also, condensate and residue unavoidably build up and crack near the cover seat so that the inner cover also becomes encrusted. When this occurs, a considerable force must be exerted sometimes requiring the assistance of a braker rod to open the cover.